This invention relates to transmission of data using an asymmetric digital subscriber line (ADSL) channel and, more particularly, to methods and apparatus for transmitting data to and between an ADSL channel and an Ethernet network.
The rapid growth of the xe2x80x9cinformation highwayxe2x80x9d has created the need for high-speed, low-cost techniques for transmitting data to and from homes, small businesses, schools and the like. At the data rates of conventional modems, the transmission of detailed graphics, for example, typically requires a time that may be annoying to the user. A web page containing detailed graphics of 100 kilobytes may require 27 seconds for transmission. Optical fiber networks and CATV networks have sufficient bandwidth to permit high speed data transmission. However, the infrastructure is not presently available to provide data services to consumers on optical fiber or CATV networks on a widespread basis and at low cost.
An ADSL standard for data transmission is being developed to address these issues. Data transmission, according to the ADSL standard, permits transmission of simplex and duplex digital data signals over the conventional twisted wire pairs that are used for plain old telephone service (POTS). The digital data signals are transmitted at frequencies above the baseband analog POTS band (0-4 kilohertz). The ADSL standard is a physical layer standard providing for a simplex downstream channel at a maximum rate of 6.2 megabits per second and a minimum rate of 1.544 megabits per second. The ADSL standard also includes a duplex digital channel at optional rates of 64 kilobits per second, 160 kilobits per second, 384 kilobits per second and 576 kilobits per second. The ADSL standard takes advantage of the fact that most consumer applications, such as Internet access, access to online information services, access to private networks and work-at-home applications, require a larger bandwidth into the home than out of the home. ADSL transport technology is described by R. Olshansky in xe2x80x9cMoving Toward Low-Cost Access to the Information Highwayxe2x80x9d, Telephony, Nov. 7, 1994, pp. 31-37.
The basic ADSL architecture includes an ADSL interface unit at the telephone company central office and an ADSL interface at the customer location, interconnected by a twisted pair of conductors. Each ADSL interface unit includes a POTS splitter and an ADSL modem. The ADSL modem transmits and receives digital data on the twisted pair at the selected ADSL transmission rates. At the central office, the ADSL interface unit receives and transmits digital data from a packet switch. The POTS splitter frequency multiplexes the high speed digital data and the analog POTS signal onto the twisted pair for transmission. The POTS splitter at the customer location decouples the analog POTS signal onto the existing POTS wiring in the home. The ADSL modem adapts the ADSL data signals to the conventional 10 Base T Ethernet format and delivers them over 10 Base T wiring to the customer""s PC or Ethernet LAN. The interface between the Ethernet network and the ADSL modem must be configured to ensure a smooth and efficient transfer of digital data.
According to a first aspect of the invention, an Ethernet to ADSL adapter is provided for controlling data communication between an Ethernet port and an ADSL modern connected to an ADSL channel. The adapter comprises a first buffer for storing data packets received at the Ethernet port, means for transmitting the data packets from the first buffer to the ADSL modem at a first ADSL transmission rate and means for transmitting data packets received from the ADSL modem to the Ethernet port at a second ADSL transmission rate. The adapter further comprises means for transmitting a jamming signal from the Ethernet port when the first buffer contains a first predetermined number of data packets and data packets are not available for transmission to the Ethernet port. Transmission of additional data packets to the Ethernet port by other Ethernet nodes is inhibited by the jamming signal.
Preferably, the adapter includes means for inhibiting transmission of data packets to the ADSL modem when a first pause signal is received from the ADSL modem. The adapter may include means for resuming transmission of data packets to the ADSL modem in response a resume signal received from the ADSL modem following receipt of the first pause signal. The adapter may further include a timer for generating a timeout signal in response to the first pause signal, the timing signal representing a timeout period, and means responsive to the timeout signal for resuming transmission of data packets to the ADSL modem following the timeout period.
In a preferred embodiment, the adapter further includes a second buffer for storing the data packets received from the ADSL modem, wherein data packets are transmitted to the Ethernet port from the second buffer, and means for transmitting a second pause signal to the ADSL modem when the second buffer contains a second predetermined number of data packets. Transmission of additional data packets to the adapter from the ADSL modem is inhibited by the second pause signal. The adapter may further include means for transmitting a resume signal to the ADSL modem following transmission of the second pause signal when the second buffer contains less than the second predetermined number of data packets.
The data packets may be transmitted to the Ethernet port using binary back-off when the occupancy of the second buffer is below a threshold. The data packets may be transmitted to the Ethernet port using zero back-off when the occupancy of the second buffer is at or above the threshold.
According to another aspect of the invention, an Ethernet to ADSL adapter is provided for controlling data communication between and Ethernet port and an ADSL modem connected to an ADSL channel. The adapter comprises means for transmitting data packets received at the Ethernet port to the ADSL modem at a first ADSL transmission rate, a buffer for storing data packets received from the ADSL modem at a second ADSL transmission rate and means for transmitting the data packets from the buffer to the Ethernet port. The adapter further comprises means for transmitting a pause signal to the ADSL modem when the buffer contains a predetermined number of data packets. Transmission of additional data packets to the adapter from the ADSL modem is inhibited by the pause signal.
According to a further aspect of the invention, a method is provided for controlling data communication between an Ethernet port and an ADSL modem connected to an ADSL channel. Data packets received at the Ethernet port are stored in a first buffer, and the data packets are transmitted from the first buffer to the ADSL modem at a first ADSL transmission rate. Data packets received from the ADSL modem at a second ADSL transmission rate are transmitted to the Ethernet port. A jamming signal is transmitted from the Ethernet port when the first buffer contains a first predetermined number of data packets and data packets are not available for transmission to the Ethernet port. Transmission of additional data packets to the Ethernet port by other Ethernet nodes is inhibited by the jamming signal.
According to yet another aspect of the invention, a method is provided for controlling data communication between an Ethernet port and an ADSL modem connected to an ADSL channel. Data packets received at the Ethernet port are transmitted to the ADSL modem at a first ADSL transmission rate. Data packets received from the ADSL modem at a second ADSL transmission rate are stored in a buffer, and the data packets are transmitted from the buffer to the Ethernet port. A pause signal is transmitted to the ADSL modem when the buffer contains a predetermined number of data packets. Transmission of additional data packets to the adapter from the ADSL modem is inhibited by the pause signal.